Range based equivalent of filemap_fdatawrite for O_SYNC writers (to go with
writepages range support added to mpage_writepages).  If both <start> and
<end> are zero, then it defaults to writing back all of the mapping's dirty
pages.
Signed-off-by: Suparna Bhattacharya <suparna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>